A ballpoint pen tip has been conventionally known, in which a tip end portion of a tip body, which includes a ball holding chamber configured to hold a ball, an ink circulation hole formed in a center of a bottom wall of the ball holding chamber and a plurality of ink circulation grooves extending radially from the ink circulation hole, is caulked inside, so that a part of the ball held in the ball holding chamber projects from a tip end edge and the ball is rotatably held.
In addition, like a “ballpoint pen tip” disclosed in JP2000-71672A, a lot of ballpoint pen tips have been proposed, in which a ball seat having the same contour as that of a ball is provided on a bottom wall of a ball holding chamber, and a ball is placed on the ball seat.
In addition, JP2001-39077A discloses that, by means of a hammering process that presses a ball for forming a ball seat from the side of a tip end portion, an inside portion of the ball seat rises up due to a spring-back property of a tip metal material, so that a counterbored part, by which an outside portion of the ball seat is not in contact with the ball, can be formed.